As Voyager gets farther and farther away from the sun, why does the resistance increase?

The universe is almost a vacuum, so flying in the universe will encounter almost no resistance.

But this is only from a macroscopic perspective. In the universe, different regions have different densities, so a spacecraft flying at high speed will still encounter a certain amount of resistance. Take the solar system as an example. The closer to the sun, the greater the density of matter, while the farther away from the sun, the sparser the density of matter. However, it is interesting that the resistance encountered by the Voyager, which is moving away from the sun, has increased slightly. Why is this?

Voyager consists of two sister probes, Voyager 1 and Voyager 2, which were launched in 1977. Their goal is the distant sea of ​​stars outside the solar system. Now Voyager has been flying for more than 40 years and has flown more than 18.5 billion kilometers. However, the resistance it encounters has not decreased but increased.

Where does the flight resistance of Voyager come from? It comes from the vacuum matter.

What is vacuum matter? The term "vacuum matter" sounds somewhat contradictory, because "vacuum" means nothing. Since there is nothing, how can there be "matter"? In fact, this term cannot be separated. It is a special term that represents a space with more energy and particles. Therefore, "vacuum matter" is not really "vacuum". It's just that these particles are extremely small and invisible to the naked eye, and it looks like there is nothing. So where do these energy and particles come from? In the solar system, the closer to the sun, the denser the vacuum matter, because the sun is the producer of vacuum matter.

The solar wind releases a large number of particles every moment. These particles have extremely high energy, and this energy will gradually decay during the propagation process, so the farther away from the sun, the weaker the energy.

Obviously, as Voyager moves further and further away from the sun, the vacuum matter will become less and less, the energy will become lower and lower, and the impact on Voyager will become smaller and smaller, but the reality is not so. We call the area that the sun and the solar wind can affect the "heliosphere", and its range is about 18 billion kilometers from the center of the sun. The distance between Voyager and the sun has exceeded 18.5 billion kilometers, which is obviously beyond the range of the heliosphere. It should be completely unaffected by the solar wind, but the vacuum matter it encounters has increased dramatically. According to the data from the plasma detector carried by Voyager 2, the vacuum matter near it currently has 0.12 electrons per cubic centimeter more than when it was in the heliosphere, and this number is still increasing exponentially.

The sudden increase in vacuum matter obviously did not come from the sun, so where did it come from?

There are two mainstream views. One is that these vacuum materials come from the Oort Cloud. There is a globular nebula outside the solar system, which is composed of a large number of small celestial bodies, tightly wrapping the solar system. The large number of small celestial bodies leads to an increase in the density of matter in this area, so the closer the Voyager is to the Oort Cloud, the higher the density of the vacuum material will be. Although the Oort Cloud is located outside the solar system, it still belongs to the solar system in essence.

The second view is that the vacuum matter encountered by Voyager comes from distant interstellar space and is blown by interstellar winds.

This view holds that the vacuum matter encountered by Voyager does not come from within the solar system, but from outside the solar system. These vacuum materials blown by the interstellar wind encounter the obstruction of the solar wind when they reach the outer edge of the heliosphere, so they accumulate outside the heliosphere and become increasingly dense. If this is the reason, as Voyager continues to move forward, the density of the vacuum matter will gradually decrease, which can be verified by time.

Are there other possibilities besides these two mainstream views? Yes.

Stars that can produce vacuum matter are relatively easy to find, especially those at close range. However, the closest extrasolar star to the solar system is Proxima Centauri, 4.2 light-years away, so the vacuum matter here does not come from stars.

If vacuum matter doesn't come from stars, where does it come from? Maybe it comes from an alien civilization.

Vacuum matter is energy and particles. If there is energy, there may be life. If there is an advanced alien civilization or a cluster of alien civilizations outside the solar system, it may also lead to an increase in the surrounding vacuum matter. Of course, this idea is rather unrealistic and seems a bit unrealistic compared to the mainstream view, but the universe is so big, who can say for sure? If there is really an alien civilization nearby, then maybe they will contact us soon, because there is a copper-plated gold record recording human civilization on the Voyager. If the Voyager is intercepted by them, they will get this record and learn about the existence of Earth civilization through this record.

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